High pressure feeder having smooth pocket in rotor

ABSTRACT

A high pressure transfer device has a rotor mounted in a housing for rotation with respect to inlet and outlet ports and having through going pockets. The pockets have interior surface configurations substantially devoid of nooks, crannies, and related flow restrictions. This can be accomplished by providing inserts in the pockets, or by constructing the pockets so that there are substantially smooth interior wall tubes extending from one end of the rotor and the other and cooperating with an inlet and an outlet at the same time. Using the high pressure transfer device to feed wood chips or the like in a slurry using a high pressure transfer pump can result in flow through the rotor pockets that is more uniform by at least 5% compared to in conventional high pressure transfer devices.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is based upon provisional application serial No.60/133,669 filed May 11, 1999, the disclosure of which is incorporatedby reference herein.

BACKGROUND AND SUMMARY OF THE INVENTION

[0002] In the processing of comminuted cellulosic fibrous material, forexample, wood chips, to produce cellulose pulp, one of the somewhatessential devices used to introduce a pressurized slurry of material toa treatment vessel is what is known in the art as the High PressureFeeder (“HPF”). The HPF is a rotary valve-type device that, with the aidof a high-pressure pump, transfers a slurry of material and liquid atone pressure for example, between about 0 to 2 bar gauge, to a secondhigher pressure, for example, between about 5-15 bar gauge, at whichtreatment of the material is most desired. One advantageous function ofthis device is the capability to act as an pressure isolation device.Should a disruption in the operation of the digester or the feed systemoccur, the HPF prevents the high-pressure medium from escaping to thelow-pressure medium or to the surrounding environment.

[0003] Since the early development of the continuous cooking process bythe late Johan Richter and others (as documented in Mr. Richter's TheHistory of Continuous Cooking [1981]), the HPF has been an essentialfeature of the feed system of the continuous digester. In this 1981publication Mr. Richter documented the early development of the HPF, inparticular some early designs are shown in FIGS. 17,18, 21, and 22 ofthis publication. Rydholm also documents one early “balanced rotor” HPFdesign in FIG. 1.1 of the 1970 publication Continuous Pulping Processes.The development of HPF design is also documented in U.S. Pat. Nos.2,459,180; 2,688,416; 2,870,009; 2,901,149; 2,914,223; 3,041,232;4,033,811; 4,338,049; 4,430,029; 4,508,473; and 4,516,887. Not until therecent development of the slurry-type pumping of the material by Prough,et al., as described in U.S. Pat. Nos. 5,476,572; 5,622,598; 5,635,025;5,736,006; 5,753,075; 5,766,418; and 5,795,438 and marketed under thename LO-LEVEL® Feed System by Ahistrom Machinery Inc. of Glens Falls,N.Y., has the elimination of the HPF and pumping directly to thetreatment vessel been technically feasible.

[0004] However, the present design of the HPF, as exemplified by thedesigns shown in U.S. Pat. Nos. 5,236,285 and 5,236,286, has notprogressed significantly since the earlier designs developed by Richter,et al. The recent development of digester feed system technology, asexemplified by the work performed in the development of the LO-LEVEL®Feed System, and documented in U.S. Pat. No. 5,476,572 and the otherpatents listed above, has resulted in new insights into the limitationsof existing HPF designs and how these limitations can be overcome byimproving the HPF as a result of these insights. The present inventionis an example of such an improvement.

[0005] As shown in FIGS. 3, 4 and 5 of U.S. Pat. No. 5,236,285, the HPFcomprises or consists of a stationary housing with a pocketedcylindrical rotor mounted for rotation in the housing. The housingincludes four ports: a high-pressure inlet port; a high-pressure outletport; a low-pressure inlet port and a low-pressure outlet port. Thelow-pressure inlet is opposite the low-pressure outlet and thehigh-pressure inlet is opposite the high-pressure outlet. As thepocketed rotor (driven by a variable speed motor and gear reducer)rotates in the housing, the through-going pockets of the rotorsequentially communicate with the four ports of the housing. Typically,the rotor contains two or more through-going pockets such that differentpockets communicate with different high and low-pressure ports as therotor rotates. The unique, hydraulically-balanced design of the HPFpermits the rotor pockets to be exposed to high and low pressure fluidssimultaneously without causing a load imbalance and excessive wear ofthe rotor or its lining.

[0006] Typically, the top port of the feeder housing of the HPF is thelow-pressure inlet port into which a slurry of chips and liquid isintroduced to the feeder. This historically has been true for overthirty years since the slurry of chips and liquor have been introducedto the HPF by gravity from a conduit, known in the art as the ChipChute, mounted above the HPF. However, due to the pump-feeding whichcharacterizes the LO-LEVEL Feed System marketed by Ahlstrom MachineryInc., the pressurized slurry flow from the slurry pump may be introducedto a low-pressure inlet of the HPF which is oriented wherevernecessitated by the installation. The pump-fed slurry can be introducedto a port located physically on top, on either side, on the bottom ofthe HPF, or even to a port oriented at an oblique angle, that is, at anyangle of orientation desired. However, for the sake of illustration, thelow-pressure inlet of the HPF of the present invention will be assumedto be located on top of the feeder, for example, as shown in FIGS. 3-5of U.S. Pat. No. 5,236,285. The rotor typically rotates at a speed ofbetween about 5 to 15 rpm, preferably, between about 7 to 10 rpm,depending upon the capacity of the HPF and the production rate of thepulping system it is used to feed.

[0007] As the low-pressure slurry is introduced to the low-pressureinlet of the HPF, one or more of the through-going pockets of therotating rotor receive the slurry. As noted above, the low-pressureoutlet of the HPF is located opposite the low-pressure inlet. Therefore,as the slurry is introduced to the low-pressure inlet and the first endof one of the through-going pockets, the slurry flows into the pocketand toward the second end of the pocket, in this case, toward the lowerend of the pocket, and toward the low-pressure outlet. The low-pressureoutlet port of the HPF is typically provided with a screen element, forexample, a cast horizontal bar type screen element (see for example thescreen element 29 in U.S. Pat. No. 5,443,162). This screen elementretains the chips in the slurry within the feeder and allows some of theliquid in the slurry to pass out of the second end of the pocket andthrough the screen. This liquid typically is recirculated back to alocation upstream of the HPF. The chips that are introduced to the rotorpocket, including those chips retained by the screen element, aretransported by the rotation of the rotor. After a typical one-quarterrevolution of the rotor, the first end of the pocket that was once incommunication with the low-pressure inlet is placed in communicationwith the high pressure outlet. The high-pressure outlet typicallycommunicates with the inlet of a digester, either a continuous or batchdigester, via one or more conduits. At the same time, the rotation ofthe rotor also places the second end of the through-going pocket, whichwas just in communication with the low-pressure outlet, in communicationwith the high-pressure inlet. The high pressure inlet typically receivesa flow of high-pressure liquid from a high-pressure hydraulic pump. Thepressure of this liquid typically ranges from about 5 to 15 bar gauge,and is typically about 7-10 bar gauge. This high-pressure liquiddisplaces the slurry of chips and liquid from the through-going pocketand out of the high-pressure outlet and ultimately to the inlet of thedigester.

[0008] As the rotor continues to rotate, the second end of the pocketwhich received the high-pressure fluid then is placed in communicationwith the low-pressure inlet and receives another supply of slurry fromthe conduit connected to the low-pressure inlet. Similarly, the firstend of the pocket is rotated into communication with the low-pressureoutlet of the housing, having the screen element. The process describedabove then repeats itself such that during one complete revolution ofthe rotor each through-going pocket receives and discharges two chargesof chips and liquid. The rotor typically contains at least two,typically four, through-going pockets such that the rotor is repeatedlyreceiving slurry from the low-pressure inlet and discharging slurry outthe high-pressure outlet. The ends of the these pockets act as both aninlet for slurry and an outlet depending upon the orientation of therotor.

[0009] Over the years, certain modifications have been made to the rotoror housing in order to improve the operation or efficiency of the HPF.As shown in U.S. Pat. No. 5,236,285 one such modification was made tothe screen element in the low-pressure outlet in which the leading edgeof the screen was blanked off. As the rotor rotates, this blanking ofthe screen postpones the exposure of the pocket to the suction pressureof the pump typically attached to the low-pressure outlet of the feeder.This prevents the screen from being blinded over with small wood chips,that is, fines and pins, prior to exposing the pocket to the fullsuction of the pump below. U.S. Pat. No. 5,236,285 also discloses amodification of the high-pressure inlet which minimizes the compressionof the chips in the pocket due to the high-pressure introduced to thepocket by the high-pressure inlet. In a fashion similar to the screenmodification discussed above, this modification to the leading edge ofthe high-pressure inlet comprises or consists of a barrier, or“pre-pressurization wedge” [See item 46 of FIG. 5 of U.S. '285.], whichprevents the pocket from being exposed to high-pressure liquid, whichcan compress the chips, prior to the pocket communicating with thehigh-pressure outlet. As a result, the uncompressed chip slurry is moreeasily discharged from the pocket and out the high-pressure outlet.

[0010] U.S. Pat. No. 5,236,286 discloses a method of improving thefilling efficiency of a HPF by exposing the two sets of rotor pocketswith an isolated supply of suction at the low-pressure outlet. The pumpsuction at the low-pressure outlet is simply isolated into two separateconduits.

[0011] U.S. Pat. No. 5,443,162 discloses a method of increasing theefficiency of the HPF by increasing the spacing between horizontal barsin the screen element while stiffening the screen assembly by placing areinforcing bar at the mid-span of the bars. The increased bar spacingprovides for more open flow area and thus less undesirable pressure dropacross the screen element.

[0012] The present invention provides further improvements to theefficiency and operation of the HPF.

[0013] During development and evaluation of the LO-LEVEL Feed System, itwas discovered that the discharge of slurry from the pockets of the HPFis hampered by the geometry of the pockets. Since the rotor is exposedto both high and low pressure liquids simultaneously, in conventionalHPFs the potential of producing a load imbalance on the rotor, whichmight precipitate accelerated wear, is minimized by using a uniqueoverlapping pocket geometry. As a result, each pocket is not uniform indimension but necks-down to a minimum dimension or “throat area” as thepocket passes through the rotor. This throat area defines the minimumflow area of each pocket. However, there are regions within and outsidethe throat area where the area of flow is restricted due to the geometryof the pocket. These restrictions or “nooks and crannies” in the flowarea of the pocket limit, if not restrict, the flow through the pocket.It is possible that such narrow pocket dimensions form areas where theflow of slurry stagnates and interferes with the evacuation of slurryfrom the pocket when the pocket is exposed to the high-pressure liquidintroduced at the high-pressure inlet.

[0014] One aspect of the present invention overcomes this resistance toevacuating the pocket by providing a means for delaying the exposure ofthe pocket to the high-pressure liquid so that when the pocket isexposed to the high-pressure liquid an increased flow velocity throughthe pocket is obtained. This increased flow velocity, over a typicallyshorter period of time, aids in propelling the slurry out of the pocket,including out of the areas where the flow is restricted, so that thepocket is more thoroughly and completely emptied. For example,calculations indicate that without any form of restriction in the highpressure inlet, the inlet of the pocket would be exposed to the flow ofhigh-pressure liquid for about 1.0 secs. Under current practice, usingthe present height of the pre-pressurization wedge this exposure time isreduced to about 0.9 secs. However, using the present invention, theexposure time is further reduced to about 0.8 secs. That is, theessentially same volume of flow is passed through the pocket volume inless time such that the rate of flow is greater. This greater flow ratecan aid in the removal of slurry from the pocket, especially from therestricted flow areas of the pocket.

[0015] One form of the means for delaying the exposure of the pocket tohigh pressure liquid, and thus of achieving the desired increased flowvelocity according to the invention, is to reduce the size of theopening in the high-pressure inlet so that it is smaller thanconventional, for, example at least about 10%, preferably at least about20%, and even as much as at least about 50% smaller, than theconventional high-pressure inlet opening. This reduction in area may beachieved, in one example, by increasing the size of the“pre-pressurization wedge” disclosed in U.S. Pat. No. '285. For example,where the wedge used in conventional HPFs may be about 4.5 inches inheight above the inside surface of the high-pressure outlet, so that theopen area of the outlet is about 30% less than the largest cross-sectionof the outlet, for the present invention, the wedge height is one thatpreferably results in a reduction in outlet area of at least about 40%less, more preferably at least about 50% less than the largest open areaof the outlet. For example, compared to conventional “pre-pressurizationwedges”, a wedge used according to the present invention is preferablyabout 2 inches taller and reduces the open area of outlet by at leastabout 40% compared to the largest area of the outlet. Other structuresbesides wedges can be used, however; any conventional structure that canachieve this goal being suitable.

[0016] The invention can be effected by casting the desired structureinto the high-pressure inlet of a newly designed HPF, or existing HPFsmay be modified by welding steel blocks into the inlet and machining theblocks to the desired dimensions. These blocks or pre-machined wedgesmay also be attached by any other conventional connecting device, forexample, by a bolted connection.

[0017] In another and likely most significant embodiment of the presentinvention, the restriction in flow through the pocket is minimized byeliminating the nooks and crannies in the pocket geometry to provide amore uniform flow area. This can either be achieved by modifying anexisting pocket geometry, for example, by “filling in” the areas of thepocket that restrict flow or by fabricating new rotors havingthough-going pockets having more uniform geometry, that is, a geometrythat is substantially devoid of the flow restrictions that arecharacteristic of the prior art HPF rotors. This may even be achieved byfabricating HPF rotors using cylindrical or polygonal pipe or tubing sothat the pocket geometry becomes essentially uniform in cross sectionfrom one end of the pocket to the other. Such a fabrication has thefurther advantage of providing smoother flow surfaces, along the insideof the pipes or tubes, than are presently available in the present castrotor design.

[0018] According to one aspect of the present invention there isprovided a high pressure transfer device comprising: A housing. Apocketed rotor containing a plurality of through going pockets, therotor rotatable about a given axis of rotation and the pockets havingopposite end openings which function as both inlets and outletsdepending upon the angular position of the rotor and the pockets areprovided in at least first and second sets. A housing enclosing therotor, the housing having an exterior periphery and first through fourthports disposed around the exterior periphery thereof for registry withthe inlets to and outlets from the through going pockets, for each set;for each set the first port being opposite the third port; and thesecond port opposite the fourth port. The rotor mounted in the housingfor rotation with respect to the ports about the given axis of rotation.And, the pockets having an interior surface configuration substantiallydevoid of nooks, crannies, and related flow restrictions.

[0019] The interior surface configuration of the pockets may be definedby substantially smooth interior wall tubes. For example the tubes maybe substantially polygonal in cross-section over at least a majority ofthe length thereof, but also may be circular or elliptical. Also atleast some of the tubes may be mounted in a substantially cruciformposition within the rotor.

[0020] Alternatively the interior surface configuration comprisesinserts substantially filling pre-existing nooks, crannies, and relatedflow restriction. The inserts may be substantially solid metal, may beinitially fluid but hardenable wear resistant material such as epoxy orcement, and/or may be hollow or partially hollow metal inserts.

[0021] The first port may comprise a high pressure inlet port, and thedevice may further comprise a high pressure inlet port configurationhaving an opening adjacent the rotor at least 40% less incross-sectional area than the largest cross-sectional area of the highpressure inlet.

[0022] According to another aspect of the present invention there isprovided: a high pressure transfer device comprising: A housing. Apocketed rotor containing a plurality of through going pockets, therotor rotatable about a given axis of rotation and the pockets havingopposite end openings which function as both inlets and outletsdepending upon the angular position of the rotor and the pockets areprovided in at least first and second sets (preferably with the pocketsin each set offset from the pockets in the at least one other set). Ahousing enclosing the rotor, the housing having an exterior peripheryand first through fourth ports disposed around the exterior peripherythereof for registry with the inlets to and outlets from the throughgoing pockets, for each set; for each set the first port being oppositethe third port; and the second port opposite the fourth port. The rotormounted in the housing for rotation with respect to the ports about thegiven axis of rotation. And, the pockets defined by substantially smoothinterior wall tubes.

[0023] According to yet another aspect of the present invention there isprovided a high pressure transfer device comprising: A housing. Apocketed rotor containing a plurality of through going pockets, therotor rotatable about a given axis of rotation and the pockets havingopposite end openings which function as both inlets and outletsdepending upon the angular position of the rotor and the pockets areprovided in at least first and second sets (preferably with the pocketsin each set offset from the pockets in the at least one other set). Ahousing enclosing the rotor, the housing having an exterior peripheryand first through fourth ports disposed around the exterior peripherythereof for registry with the inlets to and outlets from the throughgoing pockets, for each set; for each set the first port being oppositethe third port; and the second port opposite the fourth port. The rotormounted in the housing for rotation with respect to the ports about thegiven axis of rotation. And, the pockets filled at side portions thereofwith flow precluding inserts.

[0024] According to yet another aspect of the present invention there isprovided a method of enhancing the flow transfer characteristics of ahigh pressure transfer device comprising: A high pressure transferdevice comprising: a housing; a pocketed rotor containing a plurality ofthrough going pockets, the rotor rotatable about a given axis ofrotation and the pockets having opposite end openings which function asboth inlets and outlets depending upon the angular position of the rotorand the pockets are provided in at least first and second sets; ahousing enclosing the rotor, the housing having an exterior peripheryand first through fourth ports disposed around the exterior peripherythereof for registry with the inlets to and outlets from the throughgoing pockets, for each set; for each set the first port being oppositethe third port; and the second port opposite the fourth port; the rotormounted in the housing for rotation with respect to the ports about thegiven axis of rotation; the method comprising: (a) Substantially fillingthe nooks, crannies, and related flow restrictions in the pockets toprovide a more uniform flow area through the pockets. And, (b) rotatingthe rotor about its axis while causing a low pressure slurry to flowfrom the second port through the rotor pockets to the fourth port, andcausing a high pressure liquid to flow from the first port through therotor pockets to the third port.

[0025] In the method (a) and (b) may be practiced so that the flow in(b) is more uniform by at least 5% (e.g. more than 10%, or even morethan 15%) than if (a) were not practiced. In the practice of the method(a) may be practiced filling the nooks, crannies, and related flowrestrictions with a substantially solid metal, or with an initiallyfluid but hardenable wear resistant material, or with an at leastpartially hollow insert.

[0026] According to yet another aspect of the present invention there isprovided a method of constructing and operating a high pressure transferdevice comprising a housing having opposite first and third ports, andopposite second and fourth ports and a rotor mounted for rotation withinthe housing, the method comprising: (a) Providing at least two tubesdefining substantially smooth interior wall through extending pockets inthe rotor. And, (b) rotating the rotor about its axis while causing alow pressure slurry to flow from the second port through the rotorpockets to the fourth port, and causing a high pressure liquid to flowfrom the first port through the rotor pockets to the third port.

[0027] In the practice of the method described above, (a) may beaccomplished by mounting at least two tubes in a substantially cruciformposition in the rotor. Further (a) may be practiced using substantiallypolygon cross-section tubes, or circular or elliptical cross-sectiontubes.

[0028] It is the primary object of the present invention to provide forenhanced operation and flow of a high pressure transfer device. This andother objects of the invention will become clear from an inspection ofthe detailed description of the invention and from the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029]FIG. 1 schematically illustrates the ideal filling of a HPF pocketin by the prior art;

[0030]FIG. 2 is a view like FIG. 1 only showing the ideal emptying of aHPF pocket, and illustrating the HPF connected to the top of acontinuous digester;

[0031]FIG. 3 is a perspective view of the HPF of FIGS. 1 and 2;

[0032]FIG. 4 is an exploded perspective view illustrating certain partsof the HPF shown in FIG. 3;

[0033]FIG. 5 is an end view, partly in cross section and partly inelevation, of an exemplary HPF according to the prior art;

[0034]FIG. 6 is a view like FIG. 5 illustrating one aspect of thepresent invention;

[0035]FIGS. 7 and 8 are detail views illustrating two embodiments of theinvention shown in FIG. 6 as implemented in an existing prior art HPF;

[0036]FIG. 9 schematically illustrates a cross section of an HPF rotorpocket according to one embodiment of the present invention;

[0037]FIG. 10 is a sectional view taken along lines 10-10 of FIG. 9;

[0038]FIG. 11 is a view like FIG. 9 for another embodiment of thepresent invention;

[0039]FIG. 12 is a sectional view like FIG. 10 taken along lines 12-12of FIG. 11;

[0040]FIGS. 13 and 14 schematically illustrate a further embodiment ofthe present invention; and

[0041]FIG. 15 is a schematic perspective computer generated view ofone-quarter of an HPF rotor.

DETAILED DESCRIPTION OF THE DRAWINGS

[0042]FIGS. 1 through 4 illustrate the structure and operation of aconventional HPF, as sold by Ahistrom Machinery Inc., as defined by theprior art. FIGS. 1 and 2 schematically illustrate the operation of ahigh pressure transfer device, shown generally by reference numeral 10,according to the prior art. As is conventional, the low pressure inletport 13 of device 10 is connected to a Chip Chute or Chip Tube 11, whichis supplied with steamed chips from a conventional steaming vessel, forexample, from a horizontal screw-type steaming vessel or from aDiamondback® steaming vessel, marketed by Ahlstrom Machinery Inc, ofGlens Falls, N.Y. If a Diamondback® or similar type vessel is used aslurry of chips and liquor may be transferred and pressurized by aslurry-type pump, for example, a Wemco® screw-type slurry pump or aLawrence slurry pump. The chips are typically slurried by a source ofliquid, for example, from line 12. The chute or tube 11 is connected tothe low-pressure inlet port 13 of a metal housing 14. The housing 14also has a high-pressure inlet port 15, a low-pressure outlet port 16,and a high-pressure outlet port 17, disposed at approximately 90°intervals in the direction of rotation 18 (the direction of rotation isnot particularly important and could either be in the direction 18, oropposite thereto) of a pocketed, tapered, metal rotor 19 disposed withinthe housing 14. The rotor 19 has first and second sets of throughextending pockets (see FIG. 4), and the housing has a port (or portsegment) associated with each set.

[0043] Connected to the high-pressure inlet port 15 is a device forsupplying high pressure liquid, typically the conventional high pressurepump 20. As illustrated in FIG. 2, the pump 20 provides liquid underhigh pressure so that when the port 15 is in communication with a pocket21 within the rotor 19 the chips or like cellulosic fibrous materialwithin the pocket 21 are flushed out the high-pressure outlet port 17into conduit 22, for example, the conduit known in the art as the “topcirculation line”, associated with a conventional continuous digester23, though the digester may also be a batch digester. The line 22 feedsthe slurry of chips and liquid under pressure to the top 24 of thedigester 23. At the top 24 a conventional solids/liquid separator, forexample, a device known in the art as a “top separator” or an “invertedtop separator” (not shown) is provided. This separator returns some ofthe liquid slurrying the chips in the line 22, via the conduit 25, whichis ultimately connected to the inlet of the pump 20. The liquid in lines22, 25 typically is a combination of cooking liquor, for example, kraftwhite liquor, wood moisture, steam condensate, and sometimes blackliquor, and which may be supplemented from the make up line 26. Fornon-kraft situations, the liquid in lines 22, 25 could be water, sulfitecooking liquor, or solvent pulping liquid, among others.

[0044] Connected to the low pressure outlet port 16, and providing asuction thereto, is a line 27 connected to a low pressure pump 28, thepump 28 in turn being connected to the line 12 to supply slurryingliquid to the chip chute 11. If the device 10 is fed by a slurry-typepump as described above, the pump 28 is no longer necessary since theslurry is sufficiently pressurized by the slurry pump.

[0045] Mounted within the housing 14 at the low pressure outlet port 16is a screen, typically, one of the two screens shown generally byreference numeral 29. As seen in FIG. 1, the screens 29 allow liquid topass into the conduit 27 under the influence of the suction of pump 28,or the pressure of an upstream slurry pump, while the chips or likecellulosic fibrous material cannot pass through the screen 29 and,therefore, remain in pocket 21 in rotor 19.

[0046]FIG. 4 illustrates the rotor 19, which is tapered from a first end31 thereof to the second end 32; a housing liner 14′, mounted withinhousing 14; and one of at least two screens 29. The rotor 31 includes aplurality of (e.g., four) diametrically through-going pockets 21, 21′.Typically two pockets 21 are disposed in a first set, and two pockets21′ in a second set, the sets spaced along the axis of rotation, and thepockets of one set are offset with respect to the pockets of the other.The liner 14′ includes assorted openings 46 which communicate with rotorpockets 20, 21′, and housing ports 13, 15,16 and 17.

[0047] As shown in FIG. 3, a plug clearance adjustment mechanism 33 canbe provided for adjusting the tapered rotor 19 within the housing liner14′ which is mounted within a housing 50, and the housing 50 may beprovided with a plurality of other conventional components such as abell housing equalization line 34, a white liquor purge connection 35, apreheat header 36, and a shaft 37—connected to a power source forrotating the rotor 19 and to the rotor itself.

[0048]FIG. 5 is a cross section of the housing 50 shown in FIG. 3 asviewed from the end of the housing having the hand-wheel 33. FIG. 5illustrates the relative location of the low-pressure inlet 51,low-pressure outlet 53, high-pressure inlet 54 and high-pressure outlet52 of housing 50. The rotor (not shown, see item 19 in FIG. 4) rotatesin the housing in the direction of arrow 118. Note that the insidesurface 56 of housing 50 is shown as a broken line to represent thetapered geometry of this internal surface—inside surface 56 of thehousing and the outside surface of the rotor 19 (FIG. 4) are tapered sothat the rotor position can be axially adjusted to optimize theclearance between the housing liner and the rotor.

[0049]FIG. 5 illustrates the location of the “pre-pressurization wedge”55 in the high-pressure inlet 54 according to the prior art. This wedgeeffectively reduces the height of the inlet from height 60 to height 61.This wedge delays the exposure of the rotor pocket (see FIG. 4), whichapproaches inlet 54 in the direction of arrow 118, so that thecompression of the chips in the pocket is minimized before exposing thechips to the full pump pressure provided by pump 20 (see FIG. 1).

[0050]FIG. 6 illustrates one embodiment of the present invention. InFIG. 6, the HPF housing 150 includes a low-pressure inlet port 151, alow-pressure outlet port 153, a high-pressure inlet port 154, and ahigh-pressure outlet port 152. The rotor (not shown) rotates in housing150 in the direction of arrow 218. According to the present invention,the high pressure inlet port 154 is further modified compared to theprior art by introducing a further restriction 155 in the high-pressureinlet port 154. This restriction 155 reduces the open area of port 154from its largest height 160 to a height of 162, that is, to a heighteven smaller than the height of the prior art pre-pressurization wedge161, so that the cross-sectional area at 162 is at least 40% (preferablyat least 50%) less than at 160.

[0051]FIGS. 7 and 8 illustrate two methods of modifying an existinghigh-pressure inlet port (that is, retrofitting an existing HPF) toeffect the desired invention. In FIG. 7, high-pressure inlet 354 of aHPF, having a rotor rotating in the direction of arrow 318 and awear-resistant liner 70 (14′ in FIG. 4), is modified by introducing awelded structure 355 to the inlet 354. In this embodiment, the weldedstructure 355 consists or comprises a block 360 and a plate 361 weldedto inlet 354. After welding the structure 355 into the inlet, thestructure 355 is machined so that the inside diameter of structure 355substantially conforms to the inside diameter of liner 70.

[0052] Similarly, FIG. 8 illustrates a HPF having a high-pressure inlet454, a rotor rotating in the direction of arrow 418 and a wear-resistantliner 71. The inlet 454 is modified by introducing a welded structure455 to the inlet. In this embodiment, the welded structure 455 consistsof or comprises a block 460 welded to inlet 454. After welding thestructure 455 into the inlet, the structure 455 is machined so that theinside diameter of structure 455 substantially conforms to the insidediameter of liner 71.

[0053] FIGS. 9-12 illustrate another embodiment of the present inventionin which the through-extending pockets of the HPF are modified tominimize or eliminate the restricted flow areas so that the slurry ofmaterial can more readily pass through the pocket. In FIGS. 9-12components comparable to those in FIGS. 1-4 are shown by the samereference numeral preceded by a “1”.

[0054]FIGS. 9 and 10 illustrate cross sectional views of the rotor 19(see FIG. 4) modified according to one embodiment of the presentinvention. FIG. 9 is an end view taken, for example, from end 32 ofrotor 19 (again, see FIG. 4)—in which the end plate (118 in FIG. 10) ofthe rotor has been removed for clarity of illustration of the rotor 119interior. FIG. 10 is a cross sectional view taken through the section10-10 of FIG. 9. In FIG. 10 only one-half of the rotor 119 is shown; anessentially identical section of the rotor is omitted for clarity. Rotor119 includes an external shell 114; two end plates 118, 118′; and twothrough extending pockets 121, 121′, having respective inlets 122, 122′and outlets 123, 123′. (Of course the inlet or outlet function of theseopening will vary depending upon the orientation of the rotor 119 withinthe housing 14.) As is typical, the inlet 122 and outlet 123 of pocket121 are positioned at essentially 90 degrees from inlet 122′ and outlet123′ of pocket 121′. As is also conventional, the pockets 121, 121′ areseparated by a membrane or septum 124 which is shown clearly in crosssection in FIG. 10. FIG. 10 also illustrates how the membrane interfaceswith the internal shell wall 114′ by lines 127, 128 (shown in phantom)and lines 127′, 128′. According to one embodiment of the presentinvention, the narrow, restricted flow areas of the pockets are filledby inserts 125, 126, 125′, 126′ (not shown) to streamline the flow paththrough the pockets 121, 121′. The inserts 125, etc., fill up the nooks,crannies, and related flow restrictions, so that the pocket issubstantially devoid of them. This streamlining of the pockets 121, 121′minimizes the restriction in flow and promotes more uniform and completedischarge of the rotor pocket when filled, as shown in FIG. 1, andemptied, as shown in FIG. 2. The inserts 125, etc., may be solid, orhave a solid exterior and hollow interior.

[0055]FIGS. 11 and 12 are also cross sectional views of a rotor 219similar to the rotor 119 of FIGS. 9 and 10. In FIGS. 11 and 12components comparable to those of FIGS. 1-4 are shown by the samereference numeral only preceded by a “2”. FIG. 12 is a section of FIG.11 taken along lines 12-12. As in FIGS. 9 and 10, FIGS. 11 and 12 show arotor 219 having a shell 214; end plates 218, 218′; pockets 221, 221′having inlets 222, 222′ and outlets 223, 223′; and a membrane 224.According to the present invention, FIGS. 11 and 12 also illustrate howthe flow paths of a conventional rotor pockets can be modified byfilling the pocket cavities as shown by inserts 225, 226, 225′, and226′. The flow path modifications shown in FIGS. 9 through 12 may beused alone or in combination. For example, when the flow paths aremodified as shown in FIGS. 9 and 10 and as shown in FIGS. 11 and 12, theleast obstructed flow path having the fewest recesses can be obtained.

[0056] When the modifications shown in FIGS. 9-12 are made, the areaswhere flow restrictions may hinder the flow of material through thepocket are minimized or eliminated, being filled by the inserts 125,225, etc. These modifications may be made to newly fabricated rotors ormay be made to existing rotors For example, the modifications shown inFIGS. 9-12 may be made by applying weld overlay to the existingstructures or by fastening (for example, by welding, bolting, or otherconventional fastening mechanisms) structures, such as steel plate, tothe pocket of a new or existing rotor to conform to the desired shape.If available or feasible, an epoxy, resin, cement, or other similarinitially fluid but hardenable wear resistant material. The material maybe applied to the internal surfaces of the pocket to form the desiredpocket geometry. Whatever structure or material is attached to thepocket, some final machining may be required to conform the geometry ofthe pocket to the desired shape. Also, according to this invention, thestructures shown in FIGS. 9-12 which fill the recesses may assume othergeometries and are not strictly limited to the geometries of thestructures shown. These structures may assume whatever shapes, hollow,solid, or partially hollow, necessary in order to provide the desiredeffect: the minimization or elimination of restrictions to flow throughthe HPF pocket.

[0057] When all the modifications shown in FIGS. 9 through 12 areincorporated into existing rotor pockets, the cross section of thepocket approaches a uniform cross section having no recesses wherematerial can accumulate and hinder flow. FIGS. 13 and 14 illustrate anextension of this concept in which the modified recesses of an existingrotor are replaced by conduits having a substantially uniform crosssection. In FIGS. 13 and 14 components comparable to those in FIGS. 1-4are shown by the same reference numerals only preceded by a “3”. Similarto FIGS. 9 through 12, FIGS. 13 and 14 illustrate a rotor 319 having ashell 314; end plates 318, 318′ and pockets 321, 321′ having inlets 322,322′ and outlets 323, 323′. However, unlike the earlier embodiments,pockets 321, 321′ are defined by conduits 331 and 332 that areessentially uniform in cross section. Though the conduits 331 and 332shown are rectangular in cross section, these conduits may assume anyappropriate cross section desired, including round or circular,elliptical, square, triangular, or another polygon, though it isdesirable to minimize the number of sharp corners or recesses wherematerial may accumulate. For example, the corners of conduits 321, 321′shown in FIGS. 13 and 14 may be rounded, beveled, or chamfered, or toinclude plates welded across the corners to minimize potential recesses.

[0058] The HPF 319 shown in FIGS. 13 and 14 may be fabricated from plateand conduit, for example, by welding, or the desired geometry may beeffected by casting or forging, whatever is most economical. One methodof providing this geometry is by using commercially available(preferably metal, such as steel) pipe or tubing or other conduit. Ifnecessary, the structural integrity of the pocket can be strengthened byintroducing intermediate supports internally or externally to theconduits shown in FIGS. 13 and 14. Any such support can be formed ormachined or coated (e.g. with a solid lubricant such aspolytetrafluoroethylene) to be substantially smooth and to provide aslittle restriction to the flow of slurry into and through the pocket aspossible. FIGS. 13 and 14 show two tubes 331, 332 mounted in asubstantially cruciform position.

[0059]FIG. 15 is an isometric view of a cross section of the geometry ofan existing HPF rotor pocket. According to one embodiment of thisinvention, this exiting rotor pocket is modified as shown in FIGS. 9-12to minimize restrictions to flow through the pocket, by substantiallyfilling the nooks, crannies, and related flow restrictions, showngenerally at 80.

[0060] While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A high pressure transfer device comprising: ahousing; a pocketed rotor containing a plurality of through goingpockets, said rotor rotatable about a given axis of rotation and saidpockets having opposite end openings which function as both inlets andoutlets depending upon the angular position of the rotor and saidpockets are provided in at least first and second sets; a housingenclosing said rotor, said housing having an exterior periphery andfirst through fourth ports disposed around the exterior peripherythereof for registry with the inlets to and outlets from said throughgoing pockets, for each set; for each set said first port being oppositesaid third port; and said second port opposite said fourth port; saidrotor mounted in said housing for rotation with respect to said portsabout said given axis of rotation; and said pockets having an interiorsurface configuration substantially devoid of nooks, crannies, andrelated flow restrictions.
 2. A transfer device as recited in claim 1wherein said interior surface configuration of said pockets is definedby substantially smooth interior wall tubes.
 3. A transfer device asrecited in claim 2 wherein each said tube is substantially polygonal,and substantially uniform in size, in cross-section over at last amajority of the length thereof.
 4. A transfer device as recited in claim2 wherein at least some of said tubes are mounted in a substantiallycruciform position within said rotor.
 5. A transfer device as recited inclaim 1 wherein said interior surface configuration comprises insertssubstantially filling pre-existing nooks, crannies, and related flowrestrictions.
 6. A transfer device as recited in claim 5 wherein saidinserts are substantially solid metal.
 7. A transfer device as recitedin claim 5 wherein said inserts are initially fluid but hardenable wearresistant material.
 8. A transfer device as recited in claim 5 whereinsaid inserts are hollow or partially hollow metal inserts.
 9. A transferdevice as recited in claim 1 wherein said first port comprises a highpressure inlet port and further comprising a high pressure inlet portconfiguration having an opening adjacent said rotor at least 40% less incross-sectional area than the largest cross-sectional area of said highpressure inlet.
 10. A high pressure transfer device comprising: ahousing; a pocketed rotor containing a plurality of through goingpockets, said rotor rotatable about a given axis of rotation and saidpockets having opposite end openings which function as both inlets andoutlets depending upon the angular position of the rotor and saidpockets are provided in at least first and second sets, with the pocketsin each set offset from the pockets in the at least one other set; ahousing enclosing said rotor, said housing having an exterior peripheryand first through fourth ports disposed around the exterior peripherythereof for registry with the inlets to and outlets from said throughgoing pockets, for each set; for each set said first port being oppositesaid third port; and said second port opposite said fourth port; saidrotor mounted in said housing for rotation with respect to said portsabout said given axis of rotation; and said pockets defined bysubstantially smooth interior wall tubes.
 11. A high pressure transferdevice comprising: a housing; a pocketed rotor containing a plurality ofthrough going pockets, said rotor rotatable about a given axis ofrotation and said pockets having opposite end openings which function asboth inlets and outlets depending upon the angular position of the rotorand said pockets are provided in at least first and second sets; ahousing enclosing said rotor, said housing having an exterior peripheryand first through fourth ports disposed around the exterior peripherythereof for registry with the inlets to and outlets from said throughgoing pockets, for each set; for each set said first port being oppositesaid third port; and said second port opposite said fourth port; saidrotor mounted in said housing for rotation with respect to said portsabout said given axis of rotation; and said pockets filled at sideportions thereof with flow precluding inserts.
 12. A method of enhancingthe flow transfer characteristics of a high pressure transfer devicecomprising: a high pressure transfer device comprising: a housing; apocketed rotor containing a plurality of through going pockets, therotor rotatable about a given axis of rotation and the pockets havingopposite end openings which function as both inlets and outletsdepending upon the angular position of the rotor and the pockets areprovided in at least first and second sets; a housing enclosing therotor, the housing having an exterior periphery and first through fourthports disposed around the exterior periphery thereof for registry withthe inlets to and outlets from the through going pockets, for each set;for each set the first port being opposite the third port; and thesecond port opposite the fourth port; the rotor mounted in the housingfor rotation with respect to the ports about the given axis of rotation;said method comprising: (a) substantially filling the nooks, crannies,and related flow restrictions in the pockets to provide a more uniformflow area through the pockets; and (b) rotating the rotor about its axiswhile causing a low pressure slurry to flow from the second port throughthe rotor pockets to the fourth port, and causing a high pressure liquidto flow from the first port through the rotor pockets to the third port.13. A method as recited in claim 12 wherein (a) and (b) are practiced sothat the flow in (b) is more uniform by at least 5% than if (a) were notpracticed.
 14. A method as recited in claim 12 wherein (a) is practicedby filling the nooks, crannies, and related flow restrictions with asubstantially solid metal.
 15. A method as recited in claim 12 wherein(a) is practiced by filling the nooks, crannies, and related flowrestrictions with an initially fluid but hardenable wear resistantmaterial.
 16. A method as recited in claim 12 wherein (a) is practicedby filling the nooks, crannies, and related flow restrictions with an atleast partly hollow insert.
 17. A method of constructing and operating ahigh pressure transfer device comprising a housing having opposite firstand third ports, and opposite second and fourth ports and a rotormounted for rotation within the housing, said method comprising: (a)providing at least two tubes defining substantially smooth interior wallthrough extending pockets in the rotor; and (b) rotating the rotor aboutits axis while causing a low pressure slurry to flow from the secondport through the rotor pockets to the fourth port, and causing a highpressure liquid to flow from the first port through the rotor pockets tothe third port.
 18. A method as recited in claim 17 wherein (a) ispracticed by mounting at least two tubes in a substantially cruciformposition in the rotor.
 19. A method as recited in claim 18 wherein (a)is practiced using substantially polygon cross-section tubes.
 20. Amethod as recited in claim 17 wherein (a) is practiced usingsubstantially polygon cross-section tubes substantially uniform incross-sectional area.